JP5064745B2 - Polypropylene resin pre-expanded particles with reduced friction noise - Google Patents

Description

  The present invention relates to a polypropylene-based pre-expanded particle that can be suitably used for the production of a polypropylene-based resin-in-mold foam-molded article used for buffer packaging materials, boxes, heat insulating materials, automobile bumper core materials, and the like. More specifically, the present invention relates to a polypropylene-based pre-expanded particle that does not substantially generate a high-frequency friction sound.

  Polypropylene-based resin foam moldings are widely used for buffer packaging materials, bumper core materials, automobile members, and the like. However, these polypropylene-based resin foam molded products and polypropylene resin pre-expanded particles have a high frequency of annoying frictional sound (curk sound) when friction occurs between the foam molded products or between other plastic products and metal products. ) May occur.

  Conventionally, as a method for preventing these frictional sounds, a method of attaching higher fatty acid amide or the like to the surface of a polypropylene resin foam (Patent Document 1), a method of attaching higher fatty acid amide or the like to the surface of a granular polyolefin foam (patent) Document 2) is disclosed. However, all of these require a step of applying a higher fatty acid amide or the like on the surface of the foam, which is disadvantageous in terms of productivity and production cost. In addition, the higher fatty acid amide adhered at the time of in-mold molding is peeled off, which causes a problem that the mold is contaminated.

  On the other hand, it is known to add a fatty acid amide to a polypropylene resin in order to adjust the cell structure of the pre-expanded particles.

  For example, for the purpose of making the cell structure of the pre-expanded particles fine and uniform by adding a fatty acid amide, a polypropylene resin particle in which a fatty acid amide is kneaded into a polypropylene resin contains a foaming agent and is then heated and foamed with steam. Polyolefin resin particles comprising a mixture of a polyolefin resin containing either a polyhydric alcohol fatty acid ester or a fatty acid amide for the purpose of production method (Patent Document 3) and uniform coarsening of cell structure of polyolefin resin pre-expanded particles The manufacturing method (patent document 4) which heat-foams with a steam after containing a foaming agent is mentioned.

Further, in Patent Document 5, for the purpose of improving the secondary workability of a polypropylene resin foam molded article, a metal salt of a fatty acid is added to a polypropylene resin having a bending rigidity of 4000 to 8000 kg / cm ² (392 to 785 MPa) and 0.05 to 3. A method of containing 0% by weight and 0.05 to 2.0% by weight of fatty acid amide is disclosed. However, when the polypyropylene-based resin particles containing fatty acid amide are dispersed in water, when using the sodium dodecylbenzenesulfonate described in the examples as a dispersion aid, the pressure-resistant container There is a tendency that dispersion of resin particles in the inside becomes unstable. Further, since the dispersant tends to remain on the surface of the pre-expanded particles obtained by this method, poor fusion tends to occur during in-mold molding.

  Further, Patent Document 6 discloses that a fatty acid amide compound is added to a polypropylene resin in an amount of 2.5 to 15 for the purpose of suppressing the generation of polypropylene powder that does not damage the polypropylene resin foamed molded article due to friction due to vibration and is peeled off by friction. A method of incorporating parts by weight is disclosed. Polypropylene powder is reduced by using monoamides such as erucic acid amide, oleic acid amide, and stearic acid amide as the fatty acid amide, but the dispersant adhering to the surface of the pre-foamed particles is not reduced. In fact, the examples of the document describe the use of linear paraffin sulfonic acid soda as a dispersion aid, but in this case, the dispersant tends to remain on the surface of the pre-foamed particles. There is a tendency for poor fusion to occur during internal molding.

As described above, there are still no polypropylene resin pre-expanded particles with reduced frictional noise and reduced adhesion dispersant on the surface of the pre-expanded particles.
JP 59-2010954 A JP-A 61-23632 JP 58-1229028 A JP-A-11-209503 JP-A-8-59876 JP 2003-49019 A

  The problem of the present invention is that when the friction occurs between the pre-foamed particles, the foam-molded bodies, or between the foam-molded body and other plastic products, metal products, etc. Is to stably provide pre-expanded polypropylene resin foam particles in which the amount of adhering dispersant on the surface is reduced.

  As a result of intensive studies to solve the above problems, the present inventors have found that polypropylene resin particles containing 0.1 to 5 parts by weight of fatty acid bisamide with respect to 100 parts by weight of polypropylene resin. Water, a dispersing agent, a dispersion aid, and a foaming agent are charged into a pressure-resistant container, the contents are heated, and then the contents are discharged in a lower-pressure atmosphere than the pressure-resistant container to produce polypropylene resin pre-expanded particles. In this case, by using a polyvalent anion as a dispersion aid, a polypropylene resin pre-foamed particle that does not generate a high frequency annoying frictional sound can be obtained, and the dispersion of the polypropylene resin particle in the pressure resistant container is stable. It was found that a polypropylene resin pre-foamed particle that can be produced in a state of the present invention and that has a small amount of dispersant remaining on the surface of the pre-foamed particle can be obtained. It led to.

In the first aspect of the present invention, polypropylene resin particles are charged with an aqueous dispersion composed of water, a dispersant, a dispersion aid, and a foaming agent in a pressure vessel, heated to a predetermined temperature, and then under pressure, A method for producing polypropylene resin pre-expanded particles obtained by releasing a mixture of the polypropylene resin particles and water in a low-pressure atmosphere than in the pressure vessel, wherein the base resin of the polypropylene resin particles is a polypropylene resin composition comprising 5 parts by weight or less than 0.1 part by weight of the fatty acid bisamide with respect polypropylene resin 100 weight parts, and is characterized by using a polyvalent anion as the dispersion aid, The present invention relates to a method for producing polypropylene resin pre-expanded particles.

As a preferred embodiment,
(1) The dispersant is a hardly water-soluble inorganic substance, and the amount of the adhering dispersant is 700 ppm or less with respect to the propylene resin pre-expanded particles,
( 2 ) As the polyvalent anion, using one or more selected from sodium hexametaphosphate, sodium polyphosphate, sodium polyacrylate, sodium silicate,
( 3 ) using sodium hexametaphosphate as the polyvalent anion,
( 4 ) The fatty acid bisamide is ethylene bis stearamide,
And a method for producing the pre-expanded polypropylene resin particles described above.

The second invention relates to a method for producing a foamed polypropylene resin molding obtained by heating by filling the polypropylene resin pre-expanded particles obtained by the process of the described in the mold.

In the polypropylene resin pre-expanded particles obtained by the production method of the present invention , annoying frictional noise having a high frequency, which is generated when friction occurs between the pre-expanded particles, is reduced. The polypropylene resin foam molded article obtained from the pre-expanded particles also reduces the frictional noise generated when friction occurs between the foam molded articles or between the foam molded article and other plastic products, metal products, and the like. Moreover, since there is little dispersing agent adhering to the surface of a polypropylene resin pre-expanded particle, the fusion bonding of the polypropylene resin foam molding obtained from this pre-expanded particle is favorable. Further, since the polypropylene resin pre-expanded particles contain fatty acid bisamide, contamination of the mold is suppressed during in-mold foam molding.

The polypropylene-based foam molded article obtained from the polypropylene-based resin pre-expanded particles obtained by the production method of the present invention is suitably used for applications requiring strength and weight reduction, for example, buffer packaging materials, bumper core materials, and automobile members. Can do.

In the present invention, the polypropylene resin particles are charged with a water-based dispersion comprising water, a dispersant, a dispersion aid, and a foaming agent in a pressure-resistant container, heated to a predetermined temperature, and then under pressure, A method for producing polypropylene resin pre-expanded particles obtained by discharging a mixture of resin particles and water into a pressure-reduced container under a low-pressure atmosphere, wherein the base resin of the polypropylene resin particles is a polypropylene resin 100. a polypropylene resin composition comprising a fatty acid bisamide 5 parts by weight or less than 0.1 part by weight relative to the weight portion, characterized by using a polyvalent anion as the dispersion aid, the polypropylene resin The present invention relates to a method for producing pre-expanded particles.

  The polypropylene resin used in the present invention is a polymer comprising propylene monomer units of 50% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more, such as a Ziegler type titanium chloride catalyst or a metallocene catalyst. Polymerized and highly stereoregular ones are preferred. Specific examples include, for example, propylene homopolymer, ethylene-propylene random copolymer, propylene-butene random copolymer, ethylene-propylene-butene random copolymer, ethylene-propylene block copolymer, maleic anhydride -Propylene random copolymer, maleic anhydride-propylene block copolymer, propylene-g-maleic anhydride graft copolymer, etc. are mentioned, and each is used alone or in combination. In particular, an ethylene-propylene random copolymer, a propylene-butene random copolymer, and an ethylene-propylene-butene random copolymer can be suitably used. Further, these polypropylene resins are preferably non-crosslinked, but crosslinked resins can also be used.

  The polypropylene resin used in the present invention preferably has a flexural rigidity measured in accordance with JIS K7106 of 900 MPa to 1700 MPa, more preferably 950 MPa to 1600 MPa. If the bending rigidity is lower than 900 MPa, the molded product tends to have a low compressive strength.

  The polypropylene resin used in the present invention has a melt index (hereinafter referred to as MI) measured at a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210, and is 0.1 g / 10 min or more and 15 g / 10 min or less. Is more preferably 2 g / 10 min or more and 12 g / 10 min or less.

  The melting point of the polypropylene resin is preferably 130 ° C. or higher and 168 ° C. or lower, more preferably 135 ° C. or higher and 160 ° C. or lower, and particularly preferably 140 ° C. or higher and 155 ° C. or lower. If the melting point is within this range, a foamed molded article having excellent moldability, mechanical strength, and heat resistance tends to be obtained. Here, the melting point in the present invention refers to a peak temperature of an endothermic peak measured by a differential scanning calorimeter, and specifically, 1 to 10 mg of polypropylene resin at a rate of 10 ° C./min from 40 ° C. to 220 ° C. The peak temperature of the endothermic peak in the DSC curve obtained when the temperature is raised, then cooled to 40 ° C. at a rate of 10 ° C./min, and again raised to 220 ° C. at a rate of 10 ° C./min.

  Examples of fatty acid bisamides used in the present invention include ethylene bis stearic acid amide, methylene bis stearic acid amide, ethylene bis erucic acid amide, ethylene bis oleic acid amide, ethylene bis linolenic acid amide, hexamethylene bis hydroxy stearic acid amide, etc. The bisamide of the fatty acid of several 14-22 is mentioned. Among them, it is preferable to use ethylene bis stearic acid amide.

  The addition amount of the fatty acid bisamide used in the present invention is 0.1 to 5 parts by weight, preferably 1.5 to 4 parts by weight, more preferably 100 parts by weight of the polypropylene resin. Is 1.5 parts by weight or more and 3 parts by weight or less. If the amount of fatty acid bisamide added is less than 0.1 parts by weight, the effect of suppressing the generation of frictional noise will not be exhibited. When the addition amount of the fatty acid bisamide exceeds 5 parts by weight, when the polypropylene resin pre-expanded particles are produced, the dispersion of the resin particles in the pressure resistant container tends to become unstable. A large amount of dispersant tends to remain on the surface.

  A known method can be used as the method for adding the fatty acid bisamide to the polypropylene resin, but among them, a method of dry blending the polypropylene resin and the fatty acid bisamide is preferable because it can be easily produced.

  Next, the manufacturing method of the polypropylene resin pre-expanded particles of the present invention will be described. The polypropylene resin to which the fatty acid bisamide is added is melted using a known method, for example, using an extruder, a kneader, a Banbury mixer (trademark), a roll or the like, and the weight of one grain is 0.2 to 10 mg. Preferably, it is processed into 0.5-6 mg polypropylene resin particles. Generally, it is preferable to melt by using an extruder and to manufacture by a strand cut method. For example, a polypropylene resin extruded in a strand form from a circular die is cooled and solidified with water, air, or the like to cut polypropylene resin particles having a desired shape.

  Moreover, the cell diameter of a polypropylene resin pre-expanded particle can be adjusted to a desired value by adding a cell nucleating agent during the production of the resin particles. As the cell nucleating agent, inorganic nucleating agents such as talc, calcium carbonate, silica, kaolin, titanium oxide, bentonite and barium sulfate are generally used. The amount of cell nucleating agent added varies depending on the type of polypropylene resin used and the type of cell nucleating agent, and cannot be specified unconditionally, but is generally 0.001 part by weight or more with respect to 100 parts by weight of polypropylene resin. It is preferable that it is below the weight part.

  Furthermore, when manufacturing the polypropylene resin particles, various additives can be added as necessary within the range not impairing the properties of the polypropylene resin. Examples of additives include: coloring agents such as carbon black and organic pigments; antistatic agents such as alkyldiethanolamides, alkyldiethanolamines, hydroxyalkylethanolamines, fatty acid monoglycerides, and fatty acid diglycerides; IRGANOX1010 (trademark), IRGANOX1076 (trademark) , IRGANOX1330 (trademark), IRGANOX1425WL (trademark), IRGANOX3114 (trademark), ULTRANOX626 (trademark) and the like hindered phenolic antioxidants; (Trademark) and other phosphorus processing stabilizers; HP-136 (trademark) and other lactone processing stabilizers; FS042 (trademark) and other Roxylamine-based processing stabilizers, metal deactivators such as IRGANOX MD1024 ™; benzotriazole-based UV absorbers such as TINUVIN326 ™ and TINUVIN327 ™; benzoate-based light stabilizers such as TINUVIN120 ™; CHIMASSORB119 ( Hindered amine light stabilizers such as ™, CHIMASSORB 944 ™, TINUVIN 622 ™, TINUVIN 770 ™; flame retardant aids such as halogen flame retardants and antimony trioxide; FLAMESTAB NOR116 ™, MELAPUR MC25 ™ Non-halogen flame retardants such as hydrotalcite, acid neutralizers such as calcium stearate; crystal nucleating agents such as IRGASTAB NA11 (trademark) and the like.

  The pre-expanded polypropylene resin particles in the present invention are charged with resin particles mainly composed of polypropylene resin and an aqueous dispersion composed of water, a dispersant, a dispersion aid and a foaming agent in a pressure-resistant container and heated to a predetermined temperature. Thereafter, the mixture is obtained by releasing the mixture of the resin particles and water under pressure under an atmosphere having a pressure lower than that in the pressure vessel. Specifically, an aqueous dispersion medium containing the resin particles, a foaming agent, a dispersant and a dispersion aid is charged into a sealed container, and the temperature is increased while stirring (hereinafter sometimes referred to as a foaming temperature). After impregnating the resin particles with a foaming agent and adding additional foaming agent as necessary, the inside of the sealed container is held at a constant pressure (hereinafter sometimes referred to as foaming pressure), and then the contents are removed from the bottom of the sealed container. An example is a method of discharging in an atmosphere lower than the internal pressure of the sealed container. The sealed container to be used is not particularly limited as long as it can withstand the pressure in the container and the temperature in the container at the time of producing the pre-foamed particles, and examples thereof include an autoclave type pressure resistant container.

  Examples of the blowing agent include aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, and normal pentane, and mixtures thereof; inorganic gases such as air, nitrogen, and carbon dioxide; and water.

  The amount of foaming agent used varies depending on the type of polypropylene resin used, the type of foaming agent, the target foaming ratio, etc., and cannot be specified unconditionally, but is generally about 2 weights per 100 parts by weight of polypropylene resin particles. It is preferable that it is 60 parts by weight or more.

  As the dispersant, for example, a poorly water-soluble inorganic compound such as basic tricalcium phosphate, basic magnesium carbonate, calcium carbonate, aluminum oxide, and kaolin is preferably used.

  It is preferable to use a polyvalent anion as the dispersion aid. Examples of the polyvalent anion include sodium hexametaphosphate, sodium polyphosphate, sodium polyacrylate, and sodium silicate. For example, when sodium dodecylbenzenesulfonate exemplified in JP-A-8-59876 or linear sodium alkylsulfonate exemplified in JP-A-2003-49019 is used as a dispersion aid, In this case, the dispersion of the resin particles tends to be unstable, and even if the dispersion is stable, the dispersant tends to remain on the surface of the pre-foamed particles, and a fusion failure tends to occur during in-mold molding.

  Among these dispersion aids, sodium hexametaphosphate is preferable because good dispersibility can be obtained.

  The amount of the dispersion aid used varies depending on the type, the type and amount of the polypropylene resin used, the foaming agent, the type of the dispersant, etc., but usually 0.01 parts by weight of the dispersion aid with respect to 100 parts by weight of water. The amount is preferably 3 parts by weight or less. When the amount of the dispersion aid is less than 0.01 parts by weight, there is a tendency that the dispersant tends to remain on the surface of the pre-foamed particles. In both cases where the amount is more than 3 parts by weight, the dispersion of the resin particles in the pressure vessel tends to be unstable.

  In order to improve the dispersibility of the polypropylene resin particles in water, it is usually preferable to use 20 to 100 parts by weight of the resin particles with respect to 100 parts by weight of water.

  The aqueous dispersion of polypropylene resin particles thus adjusted in a closed container is heated to a predetermined foaming temperature with stirring, and is maintained for a certain time, usually 5 to 180 minutes, preferably 10 to 60 minutes. At the same time, the pressure in the sealed container rises, and the foaming agent is impregnated with the resin particles. Thereafter, the foaming agent is additionally supplied until a predetermined foaming pressure is reached. Thus, an aqueous dispersion of polypropylene resin particles held at the foaming temperature and foaming pressure is released into a low-pressure atmosphere (usually atmospheric pressure) by opening a valve provided at the bottom of the sealed container. Resin pre-expanded particles can be produced.

  When the aqueous dispersion of polypropylene resin particles is discharged into a low-pressure atmosphere, it can be discharged through an opening orifice of 2 to 10 mmφ for the purpose of adjusting the flow rate and reducing the magnification variation. In some cases, the low-pressure atmosphere is filled with saturated steam for the purpose of increasing the expansion ratio.

  The foaming temperature varies depending on the melting point [Tm (° C.)] of the polypropylene resin used, the type of foaming agent, etc., and cannot be specified unconditionally, but is generally determined from the range of Tm−30 (° C.) to Tm + 10 (° C.). . The foaming pressure varies depending on the type of polypropylene resin to be used, the type of foaming agent, and the foaming ratio of the desired pre-foamed particles, and cannot be defined unconditionally, but is generally determined from the range of 1 to 8 MPa (gauge pressure). .

  The polypropylene resin pre-expanded particles of the present invention have a surface-attached dispersant amount of 700 ppm or less with respect to the propylene resin particles. The amount of the adhering dispersant referred to here is a value after the polypropylene resin pre-expanded particles are washed with water containing 0.2% by weight of sodium hexametaphosphate. By using a polyvalent anion as a dispersion aid, the amount of the adhering dispersant can be reduced. When, for example, sodium dodecylbenzene sulfonate or linear sodium alkyl sulfonate is used as the dispersion aid, the amount of the adhering dispersant cannot be reduced even if washing with 0 to 20% by weight of sodium hexametaphosphate is performed.

  The amount of the adhesion dispersant of the polypropylene resin pre-expanded particles can be measured by a known method. For example, when it is known that an inorganic dispersant having a high decomposition temperature or liquid phase chromatography (HPLC) is used, a method of ashing together the pre-foamed particles and measuring the weight of the residue can be mentioned. . For example, when the dispersing agent is tribasic calcium phosphate, an aqueous solution (colorimetric solution) containing ammonium metavanadate, ammonium molybdate and nitric acid and a predetermined amount of pre-expanded particles are placed in a conical beaker and reacted for a predetermined time, and the resulting liquid is obtained. There is a method of quantifying the phase by measuring the absorbance at 410 nm with a spectrophotometer.

  In addition, when the dispersing agent is kaolin, a predetermined amount of pre-expanded particles are put in a crucible and heated until completely ashed with a gas burner, and the weight of the ash content of the resin particles before pre-expanding is calculated. The amount of the adhering dispersant can be known by measuring.

  The polypropylene resin pre-expanded particles obtained as described above can be made into a polypropylene resin expanded foam by a conventionally known molding method. For example, a) a method in which pre-expanded particles are pressurized with an inorganic gas, impregnated with the inorganic gas in the pre-expanded particles to give a predetermined internal pressure of the pre-expanded particles, filled in a mold, and heated and fused with water vapor. B) A method in which the pre-expanded particles are compressed by gas pressure and filled in a mold, and the recovery power of the pre-expanded particles is used for heat fusion with water vapor. A method such as a method of filling a mold and heat-sealing with water vapor can be used.

  As the inorganic gas, air, nitrogen, oxygen, helium, neon, argon, carbon dioxide, or the like can be used. These may be used alone or in combination of two or more. Among these, highly versatile air and nitrogen are preferable.

  Next, the manufacturing method of the polypropylene resin pre-expanded particles and the polypropylene resin foam molded article of the present invention will be described in detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples.

  Evaluation of the pre-expanded particles and the foamed molded product was performed by the method described below.

<Anti-friction effect of pre-expanded particles>
200 cm ³ of pre-foamed particles were wrapped in 30 × 30 cm gauze and the mouth was tied, and compressed at a speed of 500 mm / min, and the sound generation at that time was heard by the side. Evaluation criteria are as follows.
A: No friction noise is generated. O: Friction noise is hardly generated, but slightly generated when compressed several times.
X: A large friction noise is generated.

<Dispersion stability in autoclave>
As an index for evaluating dispersibility, when polypropylene resin particles dispersed in an aqueous dispersion medium in an autoclave are heated to a temperature higher than the softening temperature of the polypropylene resin particles, the inside of the autoclave cannot be stirred and pre-foamed. In the case where it was possible to pre-foam, the state of the polypropylene resin particles remaining in the autoclave after pre-foaming was observed, and if two or more resin particles were adhered, dispersibility ○, if all the resin particles are not adhered to each other, the dispersibility is good and ◎.

<Friction noise prevention effect in foamed molding>
The polypropylene resin foamed molded article was moved on a horizontal acrylic resin plate at a load of 0.05 MPa at a rate of 5 cm / sec to observe the presence or absence of frictional noise. Evaluation criteria are as follows.
A: No friction noise is generated. O: Friction noise is hardly generated, but slightly generated when moved several times.
X: A large frictional noise is generated when moved.
XX: A large friction sound is generated only by compressing with a load of 0.05 MPa.

<Fusion rate of foam molding>
A polypropylene resin foam molded body having a thickness of 60 mm was provided with a notch of about 5 mm with a cutter knife, and was bent and broken along the notch. The ratio at which the expanded particles were broken on the fracture surface was determined by visual observation.

<Measurement of surface adhering dispersant amount of pre-expanded particles>
The pre-foamed particles were washed by immersing them in water containing 0.2 wt% sodium hexametaphosphate for 30 seconds.

  Pre-foamed after washing with 50.0 mL of an aqueous solution (colorimetric solution) containing 0.022% ammonium metavanadate (% by weight, the same applies hereinafter), 0.54% ammonium molybdate and 3% nitric acid and W (g). The particles were placed in a conical beaker, stirred for 1 minute, and allowed to stand for 10 minutes. The obtained liquid phase was put in a quartz cell having an optical path length of 1.0 cm, and the absorbance A (−) at 410 nm was measured with a spectrophotometer.

With respect to the same colorimetric liquid, the amount of adhering dispersant C (ppm) = 5.0 × 10 ⁴ .multidot. Using the absorbance coefficient ε (g / L · cm) at 410 nm of tricalcium phosphate measured in advance. ε · A / W was determined.

Example 1
The base resin is MI = 7/10 minutes, the melting point is 146 ° C., 100 parts by weight of random polypropylene having a bending rigidity of 1000 MPa, 2.0 parts by weight of ethylenebisstearic acid amide, and 0.3 parts by weight of talc as a cell nucleating agent. The random polypropylene, ethylenebisstearic acid amide and talc were dry blended. The dry blended mixture was melt-kneaded in an extruder, extruded into a strand shape from a circular die, cooled with water, and cut with a cutter to obtain resin particles having a weight of 1.8 mg / grain.

100 parts by weight (50 kg) of the obtained resin particles, 232 parts by weight of water, 1.25 parts by weight of basic calcium triphosphate as a dispersing agent, and 0.1 part by weight of sodium hexametaphosphate as a dispersing aid have a capacity of 0.35 m ³ . After charging in a pressure-resistant autoclave and adding 20 parts of isobutane as a foaming agent with stirring, the content of the autoclave was heated and heated to a foaming temperature of 140 ° C. Thereafter, isobutane was additionally injected and the pressure was increased to a foaming pressure of 2.2 MPa. After maintaining the foaming temperature and the foaming pressure for 30 minutes, the valve at the bottom of the autoclave was opened and the autoclave contents were passed through a 4.0 mmφ opening orifice. Release under atmospheric pressure to obtain pre-expanded particles. The pre-expanded particles obtained were impregnated with air by air pressure treatment to give an internal pressure of 0.18 to 0.22 MPaG, and then filled into a 320 × 320 × 60 mm mold, and a molding temperature of 0.30 MPaG It was heated and fused with the above steam to obtain a foamed molded product. The evaluation results are shown in Table 1.

（実施例２）
エチレンビスステアリン酸アミドを１．０重量部添加したこと以外は実施例１と同様の方法で予備発泡粒子と発泡成形体を得た。評価結果を表１に示す。

(Example 2)
Pre-expanded particles and a foamed molded article were obtained in the same manner as in Example 1 except that 1.0 part by weight of ethylenebisstearic acid amide was added. The evaluation results are shown in Table 1.

(Example 3)
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Example 1 except that 4.5 parts by weight of ethylenebisstearic acid amide was added. The evaluation results are shown in Table 1.

  As a result of Examples 1 to 3, it was possible to obtain polypropylene resin expanded particles and a polypropylene resin expanded molded article that did not generate any frictional sound without impairing the dispersion stability in the autoclave. Further, since the amount of the surface adhering dispersant of the pre-expanded particles was small, the fusion rate of the foamed molded article was as good as 80%.

Example 4
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Example 1 except that 0.3 parts by weight of ethylenebisstearic acid amide was added. The evaluation results are shown in Table 1.

  Polypropylene resin foamed particles and polypropylene resin foamed molded articles that hardly generate frictional noise could be obtained without impairing the dispersion stability in the autoclave. Further, since the amount of the surface adhering dispersant of the pre-expanded particles was small, the fusion rate of the foamed molded article was as good as 80%.

(Comparative Example 1)
Pre-expanded particles and a foamed molded article were obtained in the same manner as in Example 1 except that the dispersion aid was not added. The evaluation results are shown in Table 1.
Resin particles adhered to the inside of the autoclave were observed, but polypropylene resin foamed particles and polypropylene resin foamed molded products that did not generate any frictional noise were obtained without impairing dispersion stability. Since the amount was large, the fusion rate of the foamed molded product was as low as 5%.

(Comparative Example 2)
Pre-expanded particles and an expanded molded article were obtained in the same manner as in Example 1 except that 0.04 part of linear paraffin sodium sulfonate was added as a dispersion aid. The evaluation results are shown in Table 1.
Resin particles adhered to the inside of the autoclave were observed, but polypropylene resin foamed particles and polypropylene resin foamed molded products that did not generate any frictional noise were obtained without impairing dispersion stability. Since the amount was large, the fusion rate of the foamed molded product was as low as 5%.

(Comparative Example 3)
Except for not adding ethylenebisstearic acid amide, it was attempted to obtain pre-expanded particles in the same manner as in Example 1. However, pre-expanded particles could not be obtained due to deterioration of dispersibility in the autoclave.

(Comparative Example 4)
Pre-expanded particles and a molded foam are obtained in the same manner as in Example 1 except that ethylene bis-stearic acid amide is not added and 0.04 part of sodium linear paraffin sulfonate is added as a dispersion aid. It was. The evaluation results are shown in Table 1.

  Although resin particles adhered to the inside of the autoclave were observed, the dispersion stability was not impaired, but the resulting polypropylene resin foamed particles and polypropylene resin foamed molded products generated a large frictional sound.

Claims (6)

A polypropylene-based resin particle is charged with a water-based dispersion composed of water, a dispersant, a dispersion aid, and a foaming agent in a pressure-resistant container, heated to a predetermined temperature, and then under pressure, the polypropylene-based resin particle and water. And a method for producing pre-expanded polypropylene resin particles obtained by releasing the mixture in a low-pressure atmosphere than in the pressure vessel,
Wherein a polypropylene-based polypropylene resin composition base resin comprises less than 5 parts by weight or more 0.1 part by weight of the fatty acid bisamide with respect to 100 parts by weight of a polypropylene resin of the resin particles, and multi as the dispersing aid A method for producing polypropylene resin pre-expanded particles, wherein a valent anion is used. 2. The production of propylene resin pre-expanded particles according to claim 1, wherein the dispersant is a hardly water-soluble inorganic substance, and the amount of adhering dispersant is 700 ppm or less with respect to the propylene resin pre-expanded particles. Way . The production of polypropylene resin pre-expanded particles according to claim 1 or 2, wherein at least one selected from the group consisting of sodium hexametaphosphate, sodium polyphosphate, sodium polyacrylate, and sodium silicate is used as the polyvalent anion. Method.   The method for producing polypropylene resin pre-expanded particles according to claim 3, wherein sodium hexametaphosphate is used as the polyvalent anion. Fatty bisamide, characterized in that ethylene bis-stearic acid amide, a manufacturing method of polypropylene resin pre-expanded particles according to any one of claims 1-4. Claims 1-5 polypropylene resin pre-expanded particles obtained by the production method according to any one of was filled in a mold, characterized in that it is obtained by heating a polypropylene resin expanded molded article Manufacturing method .